1. Field of the Invention
This invention relates to a device for measuring the powder flow rate of a powder coating material or the like, and more particularly to a device for measuring a power flow rate as a change in capacity.
Moreover, this invention further relates to an apparatus and a method for supplying powder, which is applied, for example, in performing a powder coating by supplying a powder coating material to a spray gun.
2. Description the Related Art
In the field of automated powder coating, there is the necessity of always supplying a powder coating material at a constant rate so as to realize a uniform finish coating film and to efficiently utilize a coating material. Thus, there have been various methods for measuring a power flow rate. The applicant for the present application have proposed a method for measuring a powder flow rate while utilizing the measurement of the density of powder, and further have proposed an apparatus for performing such a method, in Japanese Patent Laid-Open No. 7-35591/1995. In accordance with this method, the density of powder is measured from various physical quantities such as light transmissivity, ultrasonic transmittance and electrostatic capacity. Then, the powder flow rate is measured from the measured value of the powder density. Thus, as compared with a conventional method for measuring a flow rate by detecting a pressure difference or the like, a powder flow rate can be measured according to this proposed method by using a very simple mechanism. Consequently, there can be realized a device for measuring a powder flow rate, whose manufacturing cost is low and maintenance is easily achieved, and color is easily changed.
Among the methods disclosed in the aforementioned Japanese Patent Laid-Open No. 7-35591/1995, the method of measuring the powder flow rate from change in the electrostatic capacity between a pair of measuring electrodes is extremely simple and convenient and thus can be used preferably. However, in the case of employing this method, the electrostatic capacity is susceptible to a change in the ambient temperature and may vary with the structure of the used electrodes and with the manner in which the electrodes are mounted. Moreover, the measured value of the electrostatic capacity may vary with the place through which the powder passes.
Furthermore, the powder sometimes adheres to the wall of a supply passage. This may cause variation in the quantity of supplied powder.